Build out infrastructure to share behavior tests between RDF and RDG

RDF (Request Delegate Factory) and RDG (Request Delegate Generator) have different logic for producing RequestDelegates from user handlers. However, the testing infrastructure for both approaches provides infrastructure for taking a RequestDelegate and HttpContext as input and asserting on the responses emitted. This infrastructure can be shared between the two projects so that we can construct a test library where RequestDelegates can be produced with different strategies (runtime or compile-time generation) but be run through the same tests to validate their behavior.

[JamesNK]

Low-level tests of expression trees will remain unique. Just like there are probably low-level tests for the generator, and its output.

Any test that registers a minimal API lambda and then tests running it with an HttpContext can be shared. They’re kind of like in-memory functional tests. Part of this issue will be going through the existing RDF tests and moving+updating them to be sharable.

@captainsafia Injecting a fixture would be a good way to do it. I was thinking of something simpler, like a protected abstract method on the base class, but a fixture makes it easier to reuse this pattern on multiple test files.

[captainsafia]

We’re going to close this now since the shared infrastructure has been put in place. We still need to do work to migrate tests cases, that will be handled separately as we:

• Add more features that are in parity with RDF
• Move tests over for supported feature set